WO2007108663A1

WO2007108663A1 - Lentille de fresnel et del l'utilisant

Info

Publication number: WO2007108663A1
Application number: PCT/KR2007/001423
Authority: WO
Inventors: Shinill Kang; Byungwook Kim
Original assignee: Industry-Academic Cooperation Foundation, Yonsei University
Priority date: 2006-03-23
Filing date: 2007-03-23
Publication date: 2007-09-27
Also published as: KR20070096368A; KR100804735B1

Abstract

L'invention porte sur une lentille de Fresnel dont l'angle de traînée ϑ est identique à l'angle de rayonnement Φ, et sur une DEL l'utilisant. Ladite lentille 50b, disposée devant la DEL 10 modifie le cheminement optique de sa lumière. Une couche fluorescente 30 recouvrant la DEL 10 est traversée par sa lumière. La DEL 10 émet une lumière bleue. La couche fluorescente 30, faite d'un matériau fluorescent de YAG:Ce, est plus épaisse dans le sens transversal de la DEL 10 que dans son sens longitudinal. Un réflecteur 20 en coupelle où est placée la DEL 10 renvoie vers l'avant sa lumière émise latéralement.

Description

[DESCRIPTION] [Invention Title]

FRESNEL LENS AND LED ILLUMINATING DEVICE USING IT [Technical Field] The present invention relates, in general, to a fresnel lens and a light emitting diode (LED) illuminating device using it, and more particularly, to a fresnel lens having a draft angle identical to the radiation angle of an illuminating device, and an LED illuminating device using the same. [Background Art] A light emitting diode (LED) is mainly used for a light indicator or a low-illuminance light source, and has various merits such as environmental friendliness, long lifetime, low power consumption, excellent color reproducibility, high-efficient light emission, and precision controllability. Recently, the application of the LED has been gradually increased in response to technical development enabling high brightness and miniaturization.

Illuminating devices using the LED (hereinafter, referred to as "LED illuminating device") are required to have different optical performance according to their usage. For example, the LED illuminating device used for a camera phone (i.e., a mobile phone having a built-in camera) is required to have maximum brightness characteristics within a desired radiation angle. For this purpose, the LED illuminating device should have a uniform distribution of brightness within a radiation angle, and be able to concentrically light a desired area. Furthermore, the entire LED illuminating device should be very thin to meet a demand for miniaturization. Most of the LED illuminating devices for the camera phone on the market are used without a lens attached thereto. However, a large radiation angle of the LED itself makes it difficult to intensively light only a photographing area. As an approach to overcome such a problem, the manufacturers attach a spherical lens to the LED in order to compensate for bad performance obtained by merely the LED.

FIG. 1 is a schematic elevational view illustrating the structure of a conventional LED illuminating device having an LED 10 and a spherical lens 40 attached to the LED 10.

As shown in FIG. 1, an optical path of light emitted from the LED 10 changes while the light goes through the spherical lens 40, and as a result, the light can be focused on a desired area. Thus, the illuminating device shown in FIG. 1 can compensate for bad performance obtained merely by the LED 10.

FIG. 2 is a view illustrating a distribution of illuminance of the LED illuminating device shown in FIG. 1.

As shown in FIG. 2, the illuminance distribution shows a triangular profile on the whole. This means that more light is concentrated on the center of the illuminating area, thereby resulting in poor brightness uniformity.

The illuminance of the LED has been improved in response to the development of LED manufacturing technologies, and thus the illuminating devices are easy to obtain a desired level of illuminance. In particular, with a lens attached to the LED illuminating device to collect light, high optical output power can be obtained in a desired area. However, no matter how high the brightness of illuminating device may be, the non-uniformity of brightness results in directly degrading the quality of picture images. Therefore, such brightness non-uniformity has been pointed out as a problem that should be solved.

The LED illuminating device shown in FIG. 1 has various configurations according to the desired color of light. For example, as an illuminating device for generating white light, either RGB LEDs or complementary color LEDs can be adopted. It is also possible to use an RGB fluorescent layer in combination with an ultraviolet (UV) LED or a yellow fluorescent layer in combination with a blue LED as shown in FIG. 3. FIG. 3 is a schematic elevational view illustrating the structure of a conventional LED illuminating device having a blue LED 10 and a yellow fluorescent layer 30 together with a spherical lens.

The illuminating device shown in FIG. 3 includes the blue LED 10, which replaces the LED 10 of the LED illuminating device shown in FIG. 1 , an LED cup 20, and the yellow fluorescent layer 30.

The yellow fluorescent layer 30 has a yellow epoxy resin layer containing a cerium doped yttrium aluminum garnet (YAG:Ce) fluorescent material.

FIG. 3 shows optical paths which representative reference rays emitted from the LED 10 follows. The rays excited from the front center of the LED 10 are emitted forwards, whereas the rays excited from the lateral center are emitted laterally and then are reflected forwardly by the LED cup 20.

The illuminating device shown in FIG. 3 basically has poor brightness uniformity due to the use of the spherical lens 40, and suffers from the unexpected problems as follows.

FIGS. 4, 5 and 6 are views illustrating quantitative simulation results for light radiating from the illuminating device shown in FIG. 3, in which FIG. 4 illustrates a simulation result of light emitted from the front portion of the LED 10, FIG. 5 illustrates a simulation result of light emitted from side portions of the LED 10, and FIG. 6 illustrates a combination of the results of FIGS. 4 and 5, that is, a simulation result of whole light emitted from the LED 10.

The light emitted from the side portions of the LED 10 is focused on a central ring and a surrounding ring as shown in FIG. 5. This light travels longer through the YAG:Ce fluorescent material than the light emitted from the front portion of the LED 10, and thus becomes yellowish. Accordingly, although such yellowish light mixes with the light emitted from the front portion of the LED 10, which is focused on the central ring as shown in FIG. 4, the surrounding yellow ring is still existent as shown in FIG. 6. Various approaches have been made to overcome the problems caused by the yellow ring.

For example, there is an approach to arrange another lens configuration on the bottom of the spherical lens 40, that is, the surface of the spherical lens 40 connected with the LED 10, in order to remove the yellow ring. However, the illuminating device of this configuration has a problem of poor productivity, owing to additional expense for producing a mold, additional process steps, and complicated producing process. Furthermore, the structure of the spherical lens 40 leads to increase in the size of the illuminating device, thereby degrading product competitiveness, for example, of the camera phone where the miniaturization is essential. [Disclosure] [Technical Problem]

The present invention has been made to solve the foregoing problems of the prior art and therefore an object of certain embodiments of the present invention is to provide an LED illuminating device having excellent brightness characteristics, particularly, excellent brightness uniformity within a desired radiation angle.

Another object of certain embodiments of the present invention is to provide an LED illuminating device, which is reduced in size, particularly, so as to have competitiveness meeting a demand for the miniaturization as one of the requirements of a camera phone.

Further another object of certain embodiments of the present invention is to provide an LED illuminating device, which removes a yellow ring resulting from the use of a spherical lens. [Technical Solution]

According to one aspect of the present invention, there is provided a fresnel lens, which is arranged in front of a light emitting diode to convert an optical path of light emitted from the light emitting diode, and a draft angle of the fresnel lens is identical to a radiation angle of the light whose optical path is converted by the fresnel lens.

According to another aspect of the invention, there is provided an LED illuminating device, which includes a light emitting diode; and a fresnel lens arranged in front of the light emitting diode to convert an optical path of light emitted from the light emitting diode, wherein the fresnel lens has a draft angle identical to a radiation angle of the LED illuminating device.

Preferably, the light emitting diode may include a blue light emitting diode for generating blue light.

Preferably, the illuminating device may further include a fluorescent layer covering the light emitting diode. The light emitted from the light emitting diode goes through the fluorescent layer. The fluorescent layer may contains a cerium doped yttrium aluminum garnet (YAG:Ce) fluorescent material.

Preferably, the illuminating device may further include a light emitting diode cup in which the light emitting diode is placed. The LED cup reflects light emitted laterally from the light emitting diode, in a forward direction. [Description of Drawings]

FIG. 1 is a schematic elevational view illustrating the structure of a conventional LED illuminating device having a spherical lens;

FIG. 2 is view illustrating a distribution of illuminance of the illuminating device shown in FIG. 1 ;

FIG. 3 is a schematic elevational view illustrating the structure of a conventional LED illuminating device having a blue LED and a yellow fluorescent layer together with a spherical lens;

FIGS. 4, 5 and 6 are views illustrating quantitative simulation results for light radiating from the illuminating device shown in FIG. 3, in which FIG. 4 illustrates a simulation result of light emitted from the front of the LED, FIG. 5 illustrates a simulation result of light emitted from side portions of the LED, and FIG. 6 illustrates a combination of the results of FIGS. 4 and 5, that is, a simulation result of whole light emitted from the LED; FIG. 7 is a schematic elevational view illustrating the structure of an LED illuminating device having an ordinary fresnel lens, which is a comparative example of the invention;

FIG. 8 is view illustrating a distribution of illuminance of the illuminating device shown in FIG. 7;

FIG. 9 is a schematic elevational view illustrating the structure of an LED illuminating device having a blue LED and a yellow fluorescent layer together with an ordinary fresnel lens;

FIGS. 10, 11 and 12 are views illustrating quantitative simulation results for light radiating from the illuminating device shown in FIG. 9, in which FIG. 10 illustrates a simulation result of light emitted from the front of the LED, FIG. 11 illustrates a simulation result of light emitted from side portions of the LED, and FIG. 12 illustrates a combination of the results of FIGS. 10 and 11 , that is, a simulation result of whole light emitted from the LED; FIG. 13 is a view illustrating a distribution of illuminance of the illuminating device shown in FIG. 9;

FIG. 14 is a view illustrating optical output data of the illuminating device shown in FIG. 9;

FIG. 15 is a schematic elevational view illustrating the structure of an LED illuminating device according to an embodiment of the invention;

FIG. 16 is a view illustrating a distribution of illuminance of the illuminating device shown in FIG. 16;

FIG. 17 is a schematic elevational view illustrating the structure of an LED illuminating device having a blue LED and a yellow fluorescent layer together with a fresnel lens according to another embodiment of the invention;

FIG. 18 is an exploded perspective view of the illuminating device shown in FIG. 17;

FIGS. 19, 20 and 21 are views illustrating quantitative simulation results for light radiating from the illuminating device shown in FIG. 17, in which FIG. 19 illustrates a simulation result of light emitted from the front of the LED, FIG. 20 illustrates a simulation result of light emitted from side portions of the LED, and FIG. 21 illustrates a combination of the results of FIGS. 19 and 20, that is, a simulation result of whole light emitted from the LED; FIG. 22 is a view illustrating a distribution of illuminance of the illuminating device shown in FIG. 17; and

FIG. 23 is a view illustrating optical output data of the illuminating device shown in FIG. 17. [Best Mode] The present invention will now be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown.

In designing an illuminating device, particularly, a lens, the inventor primarily designed the lens such that the illuminating device has a radiation angle Φ identical to that of a conventional illuminating device which is equipped with a spherical lens, and secondarily modified the primary design to compensate for low light output value and brightness uniformity of the illuminating device obtained by the primary design. The result of the primary design is shown in FIGS. 7 and 9, and the result of the secondary design is shown in FIGS. 15 and 17. FIG. 7 is a schematic elevational view illustrating the structure of a light emitting diode (LED) illuminating device having an ordinary fresnel lens 50, which is an intermediate model devised from an early stage of a series of developments and serves as an comparative example to an LED illuminating device according to a preferred embodiment of the invention as described below and shown in FIG. 15. In order to solve the problem with the conventional LED illuminating device equipped with the spherical lens, the inventor has carried out a series of developments and then devised the LED illuminating device, which adopts a fresnel lens 50a in place of the spherical lens 40. The fresnel lens 50a is designed such that the LED illuminating device shown in FIG. 7 has the same radiation angle Φ as the LED illuminating device shown in FIG. 1.

The illuminating device shown in FIG. 7 has some merits such as miniaturization and resultant high competitiveness. However, contrary to expectations, this illuminating device fails to enhance the uniformity of brightness as seen from FIG. 8.

FIG. 8 is view illustrating a distribution of illuminance of the illuminating device shown in FIG. 7. As shown in FIG. 8, more light is focused on the center of the illuminating device, which leads to worse results than the illuminating device having the spherical lens shown in FIG. 1.

FIG. 9 is a schematic elevational view illustrating the structure of an LED illuminating device having a blue LED 10 and a yellow fluorescent layer 30 together with an ordinary fresnel lens 50a.

As shown in FIG. 9, representative rays emitted from the front and side portions of the LED 10 pass through the fresnel lens 50a along various paths.

The illuminating device shown in FIG. 9 has components the same as those of the illuminating device shown in FIG. 3, except for the fresnel lens 50a replacing the spherical lens 40. This is to have the compatibility with a manufacturing process of conventional LED packages. Therefore, the LED 10, the LED cup 20, and the fluorescent layer 30 have the same structure as shown in FIG. 3.

FIGS. 10, 11 and 12 are views illustrating quantitative simulation results for light radiating from the illuminating device shown in FIG. 9, in which FIG. 10 illustrates a simulation result of light emitted from the front of the LED 10, FIG. 11 illustrates a simulation result of light emitted from side portions of the LED 10, and FIG. 12 illustrates a combination of the results of FIGS. 10 and 11 , that is, a simulation result of whole light emitted from the LED 10. Unlike FIG. 5, FIG. 11 shows that part of light emitted from the side portions of the LED 10 is focused again on the central area. This result indicates that the light creating the yellow ring is reduced, and that the output value of light focused on the surrounding ring area is decreased considerably, compared to that focused on the central area. Referring to FIG. 12 showing light emitted from the side portions of the LED 10 together with light emitted from the front portion of the LED 10, it can be seen that the yellow ring is decreased considerably.

FIGS. 13 and 14 are views illustrating illuminance distribution and optical output data of the illuminating device shown in FIG. 9. The analysis of FIGS. 13 and 14 will be given in relation with FIGS. 22 and 23 showing illuminance distribution and optical output data of an illuminating device according to a preferred embodiment of the invention.

The LED illuminating device shown in FIG. 9 can reduce the yellow ring while enabling the miniaturization thereof, which the inventor has sought to achieve. However, the LED illuminating device has poor brightness uniformity, because it adopts the fresnel lens 50a shown in FIG. 7.

Accordingly, the inventor has proposed a noble fresnel lens and an LED illuminating device, which will be described below as final models overcoming the aforementioned problems with the ordinary fresnel lens. FIG. 15 is a schematic elevational view illustrating the structure of an LED illuminating device according to a preferred embodiment of the invention.

As shown in FIG. 15, the LED illuminating device includes an LED 10 and a fresnel lens 50b.

The illuminating device shown in FIG. 15 is designed to have a radiation angle Φ, which is the same as the radiation angle Φ of the illuminating devices shown in FIGS. 1 and 7. This is because that, the radiation angle Φ of the LED illuminating device equipped with the spherical lens 40, which is currently on the market, is known to be as a optimum value capable of attaining optimal lighting performance. However, unlike the ordinary fresnel lens 50a shown in FIG. 7, the fresnel lens 50b of this invention has a draft angle θ, which is the same as the radiation angle Φ. It can be found that the draft angle θ of the fresnel lens 50b is designed the same as the radiation angle Φ, and thus the reference rays travel with no change in angle.

FIG. 16 is a view illustrating a distribution of illuminance of the illuminating device shown in FIG. 16.

Unlike the brightness distribution of FIGS. 2 and 8 approximately having a triangular profile, the illuminance distribution of FIG. 16 has a substantially trapezoidal profile. This indicates that the light is distributed relatively uniformly without being focused on the central area. Consequently, the illuminating device shown in FIG. 15 has a uniform brightness distribution.

FIG. 17 is a schematic elevational view illustrating the structure of an LED illuminating device having a blue LED 10 and a yellow fluorescent layer 30 together with a fresnel lens 50b according to another embodiment of the invention.

As shown in FIG. 17, the LED illuminating device includes the LED 10, an LED cup 20, the fluorescent layer 30 and the fresnel lens 50b.

A blue LED is used as the LED 10.

The LED 10 is seated inside the LED cup 20. The LED cup 20 functions as a support on which the LED 10 is seated, and serves to reflect the light emitted laterally from the LED 10 in the forward direction.

The fluorescent layer 30 is made of an epoxy resin layer containing a cerium doped yttrium aluminum garnet (YAG:Ce) fluorescent material. The fluorescent layer 30 is formed to cover or encapsulate the LED 10. While the light emitted from the LED goes through the fluorescent layer, it is provided with yellow color. Like the conventional LED package, the fluorescent layer 30 is set to be thicker in the lateral direction of the LED 10, compared to the forward direction of the LED 10.

The fresnel lens 50b is arranged in front of the LED 10 to convert the optical path of the light emitted from the LED 10. Blue light excited from the LED 10 is changed into white light while passing through the YAG:Ce fluorescent material, which then passes through the fresnel lens 50b to radiate at the designed radiation angle Φ.

FIG. 18 is an exploded perspective view of the illuminating device shown in FIG. 17.

FIGS. 19, 20 and 21 are views illustrating quantitative simulation results for light radiating from the illuminating device shown in FIG. 17, in which FIG. 19 illustrates a simulation result of light emitted from the front of the LED 10, FIG. 20 illustrates a simulation result of light emitted from side portions of the LED 10, and FIG. 21 illustrates a combination of the results of FIGS. 19 and 20, that is, a simulation result of whole light emitted from the LED 10.

Referring to FIGS. 19, 20 and 21 , most of light emitted from the side portions of the LED 10 is focused on the central area to mix with light emitted from the front surface of the LED 10, thereby removing a yellow ring. FIG. 22 is a view illustrating a distribution of illuminance of the illuminating device shown in FIG. 17.

In comparison between the result of FIG. 22 and the result of FIG. 13, the illuminance distribution within the radiation angle in FIG. 13 shows a large difference in the brightness between a central point and its surrounding, whereas the illuminance distribution in FIG. 22 according to the invention has a relatively uniform profile. This indicates that the brightness uniformity is improved in the invention.

Analyzing these results in relation to FIGS. 9 and 17, it can be understood that the light emitted from the relatively brighter front surface of the LED 10 is focused on the central point in FIG. 9, but is uniformly distributed within the central area in FIG. 17.

FIG. 23 is a view illustrating optical output data of the illuminating device shown in FIG. 17.

Here, the term "Error Estimate at Peak" means the standard deviation of error at the peak. The term "Number of Sample" indicates the total number of rays received by a detector. It can be found that the total number of rays of FIG. 23 is more than that of FIG. 14. The term "illuminance" indicates the brightness of light, the density of light, (i.e., the value of incident light divided by an incidence area) entering the detector. It can be also found that the average illuminance of FIG. 23 is larger than that of FIG. 14. In addition, the term "Total Flux" indicates the total flux of light (i.e., the light energy generated per unit time) received by the detector, which is also larger in FIG. 23. These data explain that light output values of FIG. 23 are larger than those of FIG. 14.

Further, the maximum illuminance of FIG. 23 is lower than that of FIG. 14, due to higher brightness uniformity.

Accordingly, it is apparent that the illuminating device shown in FIG. 17 is better than that shown in FIG. 9, in terms of the light output values and the brightness uniformity.

Claims

[CLAIMS] [Claim 1 ]

A fresnel lens arranged in front of a light emitting diode to convert an optical path of light emitted from the light emitting diode, a draft angle of the fresnel lens being identical to a radiation angle of the light whose optical path is converted by the fresnel lens. [Claim 2]

An LED illuminating device comprising: a light emitting diode; and a fresnel lens arranged in front of the light emitting diode to convert an optical path of light emitted from the light emitting diode, wherein the fresnel lens has a draft angle identical to a radiation angle of the LED illuminating device. [Claim 3] The LED illuminating device according to claim 2, wherein the light emitting diode includes a blue light emitting diode for emitting blue light, the LED illuminating device further comprising: a fluorescent layer covering the light emitting diode and containing a cerium doped yttrium aluminum garnet(YAG:Ce) fluorescent material, the light emitted from the light emitting diode going through the fluorescent layer; and a light emitting diode cup in which the light emitting diode is placed, the light emitting diode cup reflecting light emitted laterally from the light emitting diode, in a forward direction.